Froth-flotation cell

ABSTRACT

1,028,590. Froth flotation apparatus; mixing and agitating apparatus. KLOCKNER-HUMBOLDTDEUTZ A.G. Feb. 5,1964 [Feb. 21,1963], No. 4872/64. Addition to 959, 920. Headings B1C and B2H. The swash plate impeller of the froth flotation chamber described in the parent Specification is modified by the provision of ribs on its underside as well as its upper side and by providing a supply of air to both sides of the plate. As seen best in Fig. 3 the plate rotates in a cage between plates 28 and 29 with an encircling array of baffle ribs 30 to break up air bubbles. The hub 23 on which the plate is mounted provides air channels between radial fins 24 so that air drawn down from the air supply pipe 34 is not only distributed over the top of the swash plate but is drawn also underneath the plate. The float fraction is collected in launders 40 from over weirs 35. The weirs are made of rubber supported by adjustable links 36-38. Two such impellers may be at work in a single chamber and three such chambers be arranged in series as divisions of a single trough. The underflow outlet may be controlled by a needle valve.

Jan. 7, 1969 |$ENHARDT ETAL 3,420,370

FROTH-FLOTATION CELL Filed Feb. 11, 1964 Sheet of 2 IN VEN T 0R3:

752M Jan/Zaha- Jan. 7,1969 |$ENHARDT ET AL I 3,420,370-

FROTH-FLOTATION CELL Filed Feb. '11, 1964 Sheet g of 2 Fig.2

OODOOOOOOOO O O D O Fig. 3 26 30 30 INVENTORS: Kin/ (fen/[Mair fi 7cm Sal y United States Patent Us. Cl. 209-169 Int. Cl. B03d 1/02,- B01d 47/16 3 Claims Our invention relates to froth flotation cells and is an improvement over apparatus according to our copending application Ser. No. 232,179, filed Oct. 22, 1962, and now Patent No. 3,256,987, for Flotation Apparatus, assigned to the assignee of the present invention. This application is a continuation-in-part of said copending application.

In known flotation apparatus the air required for froth formation is supplied through an air pipe which extends from above the level of the particle-laden liquid down to a point above a duct or opening for incoming liquid in the lower portion of the cell vessel. A stirrer or agitator serves to impart rapid motion to the entering liquid and to beat the air into froth-forming bubbles. As a rule, the necessary amount of air is supplied to the air pipe from a compressor or other source of air under pressure since any suction elfect caused by the rotation of the stirrer is essentially incidental and far from sufficient to alone induct the required air quantity.

In contrast thereto, a flotation apparatus according to the above-mentioned copending application is capable of amply providing a sufiicient amount of froth-forming air under all operating conditions, due only to injector action which the rotating stirrer imposes upon an air supply duct traversed by the stirrer shaft. This is achieved by virtue of the fact that the lower end of the air suction duct extends freely below the location where the liquid finds access to the stirrer, so that the liquid, when being inducted by the centrifugal action of the stirrer vanes, passes downwardly along and around the lower free end of the air duct and beyond the duct opening, thus imposing a greatly increased injector action upon the ambient air.

It is an object of the present invention to further improve such flotation apparatus by greatly increasing the efliciency of the stirrer action with respect to the amount of froth-forming air inducted through the air supply pipe.

Another object of our invention is to provide a stirrer or agitator unit capable of air-inducting and froth-forming operation independently of any particular location of the liquid-supply duct, so that such a unit can be inserted into the cell vessel at any point and will then draw liquid from the vicinity of the stirrer proper in order to aerate the liquid for froth formation.

Another object of our invention, akin to the one last mentioned, is to provide a froth-forming stirrer unit that lends itself readily to being used in any desired number within a common cell vessel, thus affording or facilitating the provision of a cell battery distinguished by improved froth-floation eflicacy.

To achieve these objects, and in accordance with a feature of our invention, we provide the top side as well as the bottom side of the stirrer disc in a froth-flotation apparatus generally of the above-mentioned kind, with respective concentric arrangements of stirrer vanes, thus providing for double action of the stirrer. We furthermore provide the top as well as the bottom of the stirrer casing structure with centrally located access openings for 3,420,370 Patented Jan. 7, 1969 liquid, the top opening being located below or near the outlet opening of the air supply duct so that the liquid passing through the top opening toward the rotating stirrer flows downwardly along and around the lower, free end of the air duct to produce the above-mentioned augmented injector action.

By virtue of these features, the stirrer has a doubleacting effect which affords greatly increasing the inducted quantity of air up to about twice the amount otherwise supplied. Since the throughput of a flotation cell is largely dependent upon the quantity and distribution of the entering air, a flotation cell according to the invention possesses a considerably higher efliciency than otherwise comparable cells of the known type.

According to another feature of our invention, the stirrer comprises a disc which extends in a plane inclined to the axis of the stirrer shaft, and the vanes on the top side and bottom side of the disc have a height which decreases in the direction toward the upwardly pointing edge of the disc on the top side, whereas the height of the vanes on the bottom side decreases in the direction toward the downwardly pointing edge of the disc. As a result, the stirrer is substantially balanced, and the structure constituted by the disc inclusive of the vanes, viewed as a whole, performs only a rotating motion while preserving the tumbling action of the disc proper. The structural components of the cell that are adjacent to the body formed by the disc in the vanes, such as baflie sheets, cover plates, and the like, need only be designed in view of the simple rotational motion, so that the over-all design of the cell is considerably simplified.

According to still another feature of our invention the top side and the bottom side of the stirrer are covered by respective guide plates which form part of the abovementioned casing structure and contain the abovementioned openings through which the turbid liquid has access to the stirrer. Since at least the access opening in the top plate communicates with the outlet opening of the air supply conduit, the liquid sucked into the access opening by the action of the stirrer becomes intimately mixed with the entering air, and the mixture is centrifugally flung outwardly, while the direction of the airliquid current thus produced at any point of the disc perpihery during rotation of the disc is subjected to continuous variation on account of the inclined position of the disc. This secures a particularly intensive mixing and whirling of air and liquid in the cell vessel.

According to a further feature of our invention, the stirrer disc possesses a central hub which is radially spaced from the stirrer shaft and fastened thereto by means of ribs, pins or the like spacers. In this manner, an annular channel between the hub and the shaft is formed through which the air can pass from the top side to the bottom side of the stirrer, so that both sides of the stirrer are active in inducting an air-liquid mixture and flinging the whirling mixture into the vessel space.

Due to the intensive injection and mixing of particularly large air quantities into the turbid liquid of the cell, a flotation apparatus according to the invention lends itself particularly well for mounting a number of stirrer units in one or more rows beside each other within a single cell. Such a cell is preferably provided with a rectangular vessel, the particle-laden liquid being supplied at one narrow side, and the residual liquid being discharged from the opposite narrow side of the vessel. The cell vessel is preferably subdivided by transverse partitions into compartments, each containing two or more individual stirrer units. Such a cell possesses for a given number of stirrer units a higher power output or efficiency than an entire cell battery of the conventional types consisting of an assembly of individually complete cell vessels. Be-

sides, a multi-stirrer cell according to the invention has the advantage of greatly reducing the over-all space requirements.

It is preferable to provide each of the just-mentioned compartments in the cell vessel with a froth overflow weir of adjustable height. This takes care of the fact that as a rule the quantity of the froth to be discharged from the cell decreases from the first to the last compartment. The overflow weirs of the individual compartments are preferably designed as plates of elastic material, for example rubber, which are engaged by set screws or other adjusting devices by means of which the plates can be bent to a greater or lesser extent for the purpose of changing the active height of the weir.

The above-mentioned and more specific features of the invention will be apparent from the embodiment of a flotation cell according to the invention illustrated by way of example on the accompanying drawings, in which:

FIG. 1 shows schematically and in section a flotation cell with a number of stirrer units;

FIG. 2 shows an individual cell unit in section along theline IIII indicated in FIG. 1; and

FIG. 3 is a section along line IIIIII in FIG. 2.

As shown in FIG. 1, the flotation cell comprises an elongated vessel structure 1 whose horizontal cross-sectional shape is rectangular. A number of froth-flotation units 2 to 7 are mounted on the vessel rim beside each other. The vessel space is subdivided by transverse partitions 8 and 9, each having an opening 10, 11 for the passage of turbid liquid from one compartment to the next. The partitions 8 and 9 divide the cell vessel into three compartments each containing two froth-flotation units.

Provided at one narrow side of the cell vessel is an inlet chamber 12 to which the particle-laden liquid is supplied. The residual liquid which, for example, may contain the gangue constituents of an ore, is discharged at the opposite narrow end of the cell vessel through an opening 13 whose width can be varied be means of a control cone 14. The cone is attached to the lower end of a control rod 15 which is axially adjustable by means of a hand wheel 16. By properly setting the hand wheel 16 and hence the active cross section of opening 13, the travel time of the liquid through the cell and the level of the liquid in the cell vessel can be adjusted.

Each froth-flotation unit of the cell comprises a substantially vertical shaft 17 which is revolvably mounted in bearings 18 mounted in a supporting frame 19 on the top rim of the vessel. Secured to the upper end of the shaft 17 is a belt sheave 20 driven from an electric motor 21. Fastened to the lower end of each shaft is a stirrer disc 22 of planar shape, the plane of the disc being inclined to the shaft axis. The disc has a hub 23 fastened to the shaft 17 by spacer ribs 24 (FIG. 3) in such a manner than an annular channel space 25 remains open between shaft and hub.

The top side of the disc is provided with a concentric arrangement of stirrer vanes 26. The bottom side of the disc carries a corresponding arrangement of vanes 27. The height of the vanes on top of the disc decreases in the direction toward the upwardly pointing edge (at the right in FIG. 2) of the disc. The height of the vanes on the bottom side decreases toward the lower edge of the disc (at the left in FIG. 2). As a result the stirrer disc 22 with its vanes 26 and 27 jointly constitutes a body of substantially constant vertical height which, viewed as a whole, performs only a rotational rather than a tumbling motion when being driven by the shaft 17. However, the stirrer disc 22 as such, additionally performs a tumbling motion. The fixed components of the unit that are adjacent to the composite stirrer body need be designed only in consideration of the rotational motion of the entire stirrer body so that they can be given a relatively simple construction, as will more fully appear from the following.

Fixedly mounted at a slight distance above the vanes 26 is a guiding plate 28. A similar guiding plate 29 is mounted a slight distance below the vanes 27. The two plates are rigidly joined to each other -by bridging web pieces 30 located about the periphery of the disc 22. The bridge pieces 30 together with the two plates form substantially a casing structure for the stirrer body. The bridge pieces 30 also constitute baffle plates that promote further comminution of the air bubbles entering into the liquid, thus providing for a better distribution of the bubbles. Radial web plates 31 rigidly connect the guide plates 28 and 29 with the supporting frame structure 19.

Each guide plate has a central access opening 32, 33 for inducting flotation liquid from the cell space by the action of the stirrer body. A tubular air duct 34 surrounds the stirrer shaft 17 with radial clearance and extends from above the liquid level into the vicinity of the central access opening 32 in the upper guide plate 28. When, during rotation of the stirrer body, the vanes 26 act to induct liquid from the cell space through the top opening 32, the liquid passes downwardly along the lower end of the tubular air duct 34 and beyond the opening of this duct, thus imposing a strong injector action upon the air.

A portion of the large quantity of air thus passing through the tubular duct 34 is mixed with the liquid 1nducted through the opening 32 and is then centrifugally flung outwardly by the vanes 26 on top of the stirrer disc 22. The mixture of air and liquid then impinges against the bafile bridges 30 so that any relatively large air bubbles still contained in the mixture are beaten into small bubbles, and a good distribution of the air is secured. Another portion of the inducted air passes through the annular channel between hub 23 and stirrer shaft 17 and issues at the bottom side of the stirrer disc 22 where it is mixed with the liquid inducted through the access opening 33 in the lower guide plate 29. This portion of the air quantity is likewise flung outwardly into the cell space, due to the action of the vanes 27.

Since the stirrer disc 22 extends at an angle different from 90 with respect to the stirrer-shaft axis, the airliquid mixture issues from the periphery of the stirrer disc in continuously changing directions, seen in vertical planes. This has the eflect of producing a particularly intensive mixing of the issuing liquid-air mixture with the liquid already contained in the surrounding cell space, thus providing for intensive aeration of the liquid. The inclined position of the disc 22 and the resulting tumbling motion also promote considerably the air injection caused by the stirrer rotation, which also contributes to increasing the quantity of inducted air.

Displaceable =weirs are provided at the side walls of each compartment near the surface of the turbid bath to form an overflow for the froth. The weirs consist of respective plates 35 formed of elastic material, for example rubber. The lower edge of each plate is firmly clamped to the side wall of the compartment. Linked to the upper end of each plate by means of a pivot 36 is a control spindle 37 which can be axially displaced with the aid of screw nuts 38. In this manner, the weir plates 35 can be bent as needed for adjusting the desired height of the overflow weir.

For accelerating the draining of froth over the weir, a rotary paddle 39 is mounted in the vicinity of each weir. The paddle acts to push the froth from the bath surface toward and over the weir. Outside of the cell the froth enters into a drainage gutter 40 from which it is Withdrawn.

During operation of the flotation cell according to the invention, the turbid liquid is supplied to the entrance chamber 12, whence it passes into the first flotation compartment in which the stirrer units 2 and 3 are mounted. These units operate to distribute a large quantity of air in the liquid in fine distribution. Thus, a portion of the minerals contained in the supplied liquid is floated and separated in the first compartment. The remaining, still mineral-laden liquid passes through the opening 10 into the second compartment where the units 4 and 5 operate to subject further mineral constituents to froth-flotation. The remaining minerals, to the extent these are also to be separated by froth-flotation, are floated in the last compartment with the aid of stirrer units 6 and 7. The residual liquid passing out of the cell through the opening14 contains only the mineral particles that were to be separated from those floated in the compartments of the cell.

It will be recognized that a flotation cell according to the invention secures an extremely effective distribution of air which is inducted only by means of the stirrer units themselves and hence does not require using additional compressors or the like auxiliary means, despite the fact that exremely large quantities of air are made available. As a result, a cell of this type exhibits a high throughput together with a simple and compact design.

To those skilled in the art it will be obvious upon a study of this disclosure that our invention permits of various modifications with respect to construction and arrangement and hence can be given embodiments other than particularly illustrated and described herein, without departing from the essential features of our invention and within the scope of the claims annexed hereto.

We claim:

.1. A froth-flotation cell comprising a vessel for liquid medium, a tubular air suction duct extending downward into said vessel, said air duct having an open lower end whose outlet opening is located in the bottom portion of said vessel, a drive shaft coaxially traversing said air duct and protruding downwardly out of said outlet opening, a horizontal plate structure mounted in said vessel in fixed relationship to said duct near said outlet opening, said horizontal plate structure being formed with a hole defined by an inner marginal edge of said horizontal plate structure, said hole being of greater diameter than the diameter of said outlet opening, and said inner marginal edge substantially coaxially surrounding said outlet opening so that said inner marginal edge and said open lower end of said air duct define therebetween an annular liquidintake opening, a stirrer disc member mounted on said shaft below said plate structure and having peripherally distributed stirrer vanes on the top side as well as on the bottom side of the disc, the interior of said vessel communicating from below with said bottom side and communicating from above through said annular liquid-intake opening with said top side, whereby rotation of said stirrer member causes liquid to flow downwardly along and around the outside of said open duct end, a second horizontal plate structure fixedly mounted below said stirrer disc and having a central opening through which the interior of said vessel communicates with said bottom side of said stirrer, and baffie structures peripherally arranged about said stirrer member and rigidly joining said two plate structures to each other.

2. A froth-flotation cell comprising a vessel for liquid medium, a tubular air suction duct extending downward into said vessel, said air duct having an open lower end whose outlet opening is located in the bottom portion of said vessel, a drive shaft coaxially traversing said air duct and protruding downwardly out of said outlet opening, a horizontal plate structure mounted in said vessel in fixed relationship to said duct near said outlet opening, said horizontal plate structure being formed with a hole defined by an inner narginal edge of said horizontalplate structure, said hole being of greater diameter than the diameter of said outlet opening, and said inner marginal edge substantially coaxially surrounding said outlet open ing so that said inner marginal edge and said open lower end of said air duct define therebetween an annular liquidintake opening, a stirrer disc member mounted on said shaft below said plate structure and having peripherally distribtued stirrer vanes on the top side as well as on the bottom side of the disc, the interior of said vessel communicating from below with said bottom side and communicating from above through said annular liquid-intake opening with said top side, whereby rotation to said stirrer member causes liquid to flow downwardly along and around the outside of said open duct end, said stirrer member having a hub portion, spacer means rigidly securing said hub portion to said shaft in coaxial and radially spaced relation thereto, said shaft and hub portion forming an annular passage between said bottom side and said outlet ope-ning.

3. A froth-flotation cell, comprising a substantially rectangular vessel having liquid supply means on one of its narrow sides and liquid outlet means on the other narrow side, partition means subdividing said vessel into compartments and having respective passage means for liquid, at least one stirrer unit in each compartment, said unit having a tubular air suction duct extending downwardly into said vessel and having an open lower end whose outlet opening is located in the bottom portion of said vessel, a drive shaft coaxially traversing said air duct and pro truding downwardly out of said outlet opening, a horizontal plate structure mounted in said vessel in fixed relationship to said duct near said outlet opening, said horizontal plate structure being formed with a hole defined by an inner marginal edge of said horizontal plate structure, said hole being of greater diameter than the diameter of said outlet opening, and said inner marginal edge substantially coaxially surrounding said outlet opening so that said inner marginal edge and said open lower end of said duct define therebetween an annular liquid-intake opening, a stirrer disc member mounted on said shaft below said plate and having peripherally distributed stirrer vanes on the top side as well as on the bottom side of the disc, the interior of said vessel communimting from below with said bottom side and communicating from above through said annular liquid-intake opening with said top side, whereby rotation of said stirrer member causes liquid to flow downwardly along and around the outside of said open duct end, said passage means of said partitions comprising an overflow weir plate of adjustable height, said weir plate consisting of elastic material, and adjusting means connected with said plate for bending it in accordance with the desired height.

References Cited UNITED STATES PATENTS 2,313,654 3/1943 MacLean 209-169 2,612,358 9/1952 Daman 261-93 1,908,002 5/ 1933 Valentine 259-96 2,767,965 10/1956 Daman 209- X 2,944,802 7/ 1960 Daman 261-87 FOREIGN PATENTS 66,738 4/ 1926 Sweden.

HARRY B. THORNTON, Primary Examiner. TIM R. MILES, Assistant Examiner.

U.S. Cl. X.R. 261-93 

1. A FROTH-FLOTATION CELL COMPRISING A VESSEL FOR LIQUID MEDIUMM, A TUBULAR AIR SUCTION DUCT EXTENDING DOWNWARD INTO SAID VESSEL, SAID AIR DUCT HAVING AN OPEN LOWER END WHOSE OUTLET OPENING IS LOCATED IN THE BOTTOM PORTION OF SAID VESSEL, A DRIVE SHAFT COAXIALLY TRAVERSING SAID AIR DUCT AND PROTRUDING DOWNWARDLY OUT AND SAID OUTLET OPENING, A HORIZONTAL PLATE STRUCTURE MOUNTED IN SAID VESSEL IN FIXED RELATIONSHIP TO SAID DUCT NEAR SAID OUTLET OPENING, SAID HORIZONTAL PLATE STRUCTURE BEING FORMED WITH A HOLE DEFINED BY AN INNER MARGINAL EDGE OF SAID HORIZONTAL PLATE STRUCTURE, SAID HOLE BEING A GREATER DIAMETER THAN THE DIAMETER OF SAID OUTLET OPENING, AND SAID INNER MARGINAL EDGE SUBSTANTIALLY COAXIALLY SURROUNDING SAID OUTLET OPENING SO THAT SAID INNER MARGINAL EDGE AND SAID OPEN LOWER END OF SAID AIR DUCT DEFINE THEREBETWEEN AN ANNULAR LIQUIDINTAKE OPENING, A STIRRER DISC MEMBER MOUNTED ON SAID SHAFT BELOW SAID PLATE STRUCTURE AND HAVING PERIPHERALLY DISTRIBUTED STIRRER VANES ON THE TOP SIDE AS WELL AS ON THE BOTTOM SIDE OF THE DISC, THE INTERIOR OF SAID VESSEL COMMUNICATING FROM BELOW WITH SAID BOTTOM SIDE AND COMMUNICATING FROM ABOVE THROUGH SAID ANNULAR LIQUID-INTAKE OPENING WITH SAID TOP SIDE, WHEREBY ROTATION OF SAID STIRRER 